the authors of Proposition 208, a 1996 voter-approved initiative that set strict limits on campaign contributions. Two years ago, a federal judge prevented the initiative from taking effect after hearing constitutional arguments.

"It keeps Proposition 208 in play," Miller said yesterday, noting that California is one of only six states with no campaign contribution limits. Miller is also a leading proponent of Proposition 25, a campaign reform initiative on the March ballot. The decision is the court's first major ruling on campaign reform since 1976, when the justices upheld a $1,000 cap on individual contributions to candidates for federal office.

In yesterday's decision, the high court held that backers of the Missouri law, which set limits of $275 to $1,075 on contributions to candidates for statewide office, did not have to show evidence of that big contributors were actually corrupting election campaigns. The justices said the mere appearance of undue influence can justify reform.

"Leave the perception of impropriety unanswered, and the cynical assumption that large donors call the tune could jeopardize the willingness of voters to take part in democratic governance," wrote Justice David Souter in the court's opinion.

The justices rejected opponents' arguments that the law violated free speech rights and the right of association. But the court declined to impose any specific minimum amount that would withstand constitutional scrutiny.

The test, Souter said, is whether the contribution limitation is so strict that it prevents a candidate from mounting an effective campaign.

In the Missouri case, he said, opponents of the law did not show that the funding limits affected the candidates' ability to raise enough money.

Both supporters and opponents of California's Proposition 208 said they were encouraged by the court's ruling.

San Francisco attorney Joseph Remcho, who is representing a coalition of statewide Democratic officeholders, labor groups and the California Teachers Association, said the ruling supports their position that the limits imposed by Proposition 208 are too low.

The law sets a $250 cap on contributions for legislative seats and $500 for statewide office races.

Enforcement of the initiative was blocked two years ago by U.S. District Judge Lawrence Karlton, who said it hindered the ability of candidates to deliver their message to the voters and to mount an effective campaign.

In January 1999, the U.S. Court of Appeals refused to revive the law, saying there was no reason to disturb Karlton's preliminary injunction until the case went to trial.

"It's very good news because it's a standard we can meet," Remcho said.

But Craig Holman, co-author of Proposition 208, said the ruling was a "huge boost" for his side because the court did not require evidence of actual corruption. The justices said it is enough that voters have approved a contribution limit.

"It puts us back on very solid ground," Holman said. "It's going to have a dramatic impact in California."

Campaign reform supporters say Proposition 25 is a "fallback" if Proposition 208 is ultimately struck down. The initiative would allow public financing of political campaigns and ban corporate contributions. The law would impose a $5,000 ceiling for contributions to candidates for statewide office, $3,000 to local candidates and $25,000 to political parties.

"I'm heartened that they've reaffirmed that contribution limits can be too low," Bopp said. He said the ruling means that contribution limits of $1,000 or more are unlikely to be struck down.

For that reason, he said, Proposition 25 is "much more likely to be upheld" than Proposition 208.

Nick DeLuca, spokesman for Taxpayers for Fair Election, the group that is opposed to Proposition 25, said the decision will not help backers of the initiative because the justices did not address key issues they have raised.

"It doesn't change the fact that Proposition 25 would be an enormous step back," he said.